1. Field of the Invention
This invention relates to the design of a programmable logic controller system (which will hereinafter be referred to as a “PLC system”) and more particularly to a PLC system construction support tool for easily selecting the units making up a PLC system and examining the whole rational layout of the PLC system before the PLC system is actually constructed, and a PLC system program development support tool in which the PLC system construction support tool is included.
2. Description of the Related Art
As seen in Japanese Patent Unexamined Publication No. Hei. 8-249022, a PLC system reads an instruction command or word from a user program and performs operations on the data read from the data memory based on the address following an operand of the instruction word.
Thus, in a program development support tool, symbols described on a ladder diagram need to be converted into instruction words and operands responsive to each PLC system need to be defined using a program creation tool for creating a ladder program of the PLC system.
After such a program creation tool is used to create a program of the PLC system, how the PLC system is actually constructed introduces another problem. That is, before the PLC system is actually constructed, any desired units are selected from among available various units and it is necessary to sufficiently examine how the selected units are rationally laid out in combination, and how the relay relation is rationally set, and so forth on.